Internal-combustion engine



July 19, 1949. H. D. CARTER INTERNAL-COMBUSTION ENGINE 2 Sheets-Sheet 1Filed June 12, 1945 TIME BASE TIME BASE $5 bz: 5E 533mg Inventor ED.Ca,1-ie1= July 19, 1949. H. D. CARTER INTERNAL-COMBUST1ON ENGINE 2Sheets-Sheet 2 Filed June 12, 1945 Patented July 19, 1949 UNITED STATESPATENT OFFICE .INTERNAL-COMBUSTIbfi Enema Herbert Desmond Carter,OpenshaWQManchester,

company Application June 12, 1945, Serial No. 598,984

In Great Britain June 14, 1944 8 Claims. (Cl. 12365) .This inventionrelates to multi-cylinder twocycle internal combustion engines of theloop scavenge type and also to such engines as the uniflow, poppetvalve, opposed piston and sleeve valve types.

In such engines upon the opening of the exhaust ports, valves orsleeves, a rapid discharge of exhaust gas from the engine cylinder takesplace. This causes a rise in pressure in the form of a fundamentalexhaust pressure pulse in the exhaust branch and exhaust manifold andpipe.

This is followed by a rarefaction usually cmprising a depression inpressure below atmosphere. If the ports are opened as rapidly aspossible with as great an area as mechanically can be provided orsleeves (hereinafter referred to as port or ports) close on thecompression strokes.

The object of the present invention is to provide in an improved simpleand efficient manner for the pressure charging of the engine cylindersbefore their exhaust ports close. g

In accordance with my present invention, 1 utilise the fundamentalexhaust pressure pulse from for pressure charging another cylinder whichpreviously exhausted, just'prior to and up to the moment when itsexhaust port closes.

closing of the exhaust port of such previous cylinder, wtih the resultthat it becomes a pressure charging pulse at the latter cylnider whichtherefore receives a charge which is well above the usual air manifoldpressure. By controllnig and rephasing the fundamental exhaust pressuresure pulses to recharge such cylinder.

I prefer to pression or densification haust gases to occur in the saidprevious cylinder.

Referring to drawings:

Figure 1 is a diagram showing the pressure conditions occurring in anexhaust manifold resulting from a discharge of cylinder.

Figure 2 is a diagram ure 1 but the accompanying explanatory Figures 3and 4 are plan and elevation of an engine cylinder showing a usualarrangement of exhaust manifold.

Figures 5 and 6 are views similar to Figures 3 and 4 but showing adesign of exhaust manifold suitable for use in the application of thisinvention.,

The diagram, Figure 1, is one that might be obtained from a exhaustgases from a pheric. In a less extreme at line and closing at line C.The line E shows the rapid pressure drop in the cylinder upon a portopening, and mental pressure pulse, which results in the exhaust branchand manifold. V indicates the ensuing rarefaction which may besub-atmospheric, and P shows the abrupt rise in pressure andinterruptionof the scavenging process due to the next cylinder in sequenceexhausting, the pressure pulse having been propagated in the exhaust gasmedium from that cylinder through the exhaust branch along the manifoldand into the exhaust branch and cylinder of the previous cylinder insequence. This causes a rise in pressure in the engine cylinder asindicated by the ensuing rising part of the line at E This is followedby a drop in pressure along the fiank of the pulse P, and this pressuredrop may even be below atmospheric as is indicated at P the cylinderpressure following suit at E Thus at port closing on the line C, thepressure is subatmosit might be above atmospheric, but not appreciablyabove the pressure of the scavenging air as shown by the line A. Figure2 shows how by suitable combination of length and cross-sectional areaof branch and exhaust manifold and pipe, engine speed, indicated meanpressure and port timing, the pressure charging pulse P of thesucceeding cylinder in sequence has been controlled and re-phased inregard to F. It now occurs much later in the cycle, reachin closing. Itenters the engine cylinder and causes a rise in pressure rather abovethat of the branch due to reflection with unchanged sign from the end ofthe cylinder (or remote piston in the case of an opposed piston engine),and the cylinder pressure line E at port closing C is shown accordinglyand well above the air manifold pressure. If the pressure charging pulsefrom the succeeding cylinder in sequence is absent, the pressure in atuned system in the exhaust branch might be expected to follow thedotted lines Z shown in Figures 1 and 2. Whilst there is a positive risein pressure here, and has hitherto been used, it is eiIective only to asmall extent as compared with utilising pulse P from the next cylinderin sequence as a pressure char ing pulse.

Whilst in the above description particular reference has been made tofive and six cylinder engines, the system can be applied to any twocycle engine of the multi-cylinder type, although in practice it islikely that the engine would have to have at least three cylinders. Ingeneral the greater the number of cylinders the longer the exhaustbranches must be if a common manifold is used (as the-pressure chargingpulses are propagated from their own cylinders through the branches andpipes approximately with constant velocity at a given indicated meaneffective pressure in the exhaust gas medium), unless the manifold issplit into two or possibly more banks as may become desirable in certaincases in order to reduce the lengths of the exhaust branches required.

It is desirable that a surplus of scavenging air as compared with thecylinder volume should be provided in order to fill the exhaust branchin the region of the exhaust ports with air at each cycle, and that theexhaust branch shall be so proportioned in regard to the cross-sectionalarea and length that when the pressure charging pulse arrives at thecylinder being charged, it will cause a compression (or dens'ifi- Fshows the positive fundaits peak a little before ports cation) of airand not of exhaust gas to ensue in that engine cylinder. The surplus ofscavenging air might be increased for higher degrees of pressurecharging.

This invention is particularly valuable in regard to loop scavenge2-cycle engines as the exhaust port closing timing is fixed at the samevalue as the opening timing. Normally this results in a loss of cylindercharge down the exhaust ports. This period of loss is converted in thisinvention to a period of useful pressure charging of the cylinder.

Although for illustration the loop scavenge type of engine has beendescribed, the process is also applicable to exhaust unifiow, poppetvalve, opposed piston and sleeve valve engines. In current engines ofthe poppet, valve type or opposed piston type, it is usual to close theexhaust valves-or ports at or before point X in order to prevent anyinterference from P and to leave the air ports open a little longer toobtain a pressure charge if possible from the scavenging air which maybe increased by means such as ramming pipe effect through the air per 5.

By way of example, a S-cylinder engine may be taken with equally spacedcranks at 72 and a firing order of 1, 4, 3, 2, 5 and exhausting into acommon manifold. Suppose that Figure 1 is the diagram obtained at No. 1cylinder, the pressure charging pulse 1? (Figure 1). being that due tothe next cylinder in sequence, No. 4. On an engine with a cylinder boreof 10 the distance from the axis of No. 1 to the axis of No. 4 cylindervia the exhaust system might well be 5' 0" and the exhaust branchesapproximately 6" long. The pressure charging puls from No. 4 cylinder ispropagated to No. 1 cylinder (see Figure 3) with a velocity which mayusually be taken as lying between 1150 and 1750 ft. per second, theactual value depending generally upon the temperature, pressure andspecific volume of the gas, and is a function of the velocity of soundin the exhaust gas medium, of the exhaust gas particles and of l theexhaust gas flow in the exhaust system, but

it is found that the range of velocities hereinbefore stated givesresults which are substantially in accordance with observed results,that is to say the positions of the peaks of the pressure chargingpulses in terms of engine crank angle calculated with the use of thesaid figures will be found not to differ to an extent of more than say 5of crank shaft angle from the observed result. In the examples below afigure of 1200 ft. per second is used.

With an exhaust port timing from bottom dead centre of 70 and a speed inthe region of 340 R. P. M., the exhaust pressure charging pulse asillustrated in Figure 1 would arrive at No. 1 cylinder via the exhaustbranches B and manifold M, Figure 3 approximately 40 too early in thecycle to be used for pressure charging purposes. With port timings of64, 60 and 55 the pressure charging pulse from No.4 cylinder wouldarrive at No. 1 cylinder 28", 20 and 10 too earily respectively. Porttimings may, therefore, be used to provide correct timing of the exhaustpressure charging pulses, in this example, a 50 port timing would berequired.

Alternatively or in addition, the exhaust pulses may be re-phased byaltering the exhaust system characteristics and particularly in regardto efiective pipelengths. Thus in the above example at 340 R. P. M. thedistance over which the pressure charging pulse is propagated requiresincreasing and this increase may be effected either in the branches orthe manifold, or both. In Figure branches of increased length are shown,that is increased from about 6" as shown at B, Figure 3, to asubstantially increased value B Figure 5. In order to avoid anunnecessary stand out of the exhaust manifold M from the engine in planview, the branch pipes may be curved upwards and used in conjunctionwith an overhead exhaust manifold as shown in Figure 6 or alternativelydownwards if more convenient. Again alternatively, the branch pipes maybe grouped around a central manifold or otherwise be suitably arrangedto maintain the above characteristics, but to be of the best possibleappearance and neatness. At 340 R. P. M. and with port timings of 70,64, 60 and 55 the increase in lengths required over which the pressurecharging pulse will be propagated are approximately 280-", 200", 140"and 70" respectively at 1200 ft. per second velocity of propagation andgreater lengths at higher velocities. At 500 R. P. M. these figuresbecome 190", 135", 95" and 50", the increased lengths of the branchesthemselves being half these lengths, if the total increase is limited tothe branches only.

At 340 R. P. M. and with 5" bore pipes, pressure charging pulses at 75lb./sq. inch brake mean effective pressure can be expected to be of theorder of 5 lb./sq. inch. With a smaller exhaust pipe they will be higherand with a larger one, lower, for example, with a 6" bore pipe thepressure charging pulse may be 3 lb./sq. inch: with a 4" bore pipe itmay be 9 lbs/sq. inch and with a 9" bore pipe it may be 1 lbs/sq. in. Inanother case in a 3-cylinder engine the fundamental pulse in the exhaustbranch had an amplitude of 5 /2 l-b./sq. inch at 340 R. P. M. rising to10 lb./sq. inch at 600 R. P. M. In another case the amplitudefundamental rose from 3 ib./sq. inch at 18 lb./sq. inch brake meaneffective pressure up to 8 lb./sq. inch at 100 lb./sq. inch brake meaneffective pressure. Smaller pipe diameters and higher speeds result insome spread or increase in period of the pulses which may also beutilised in obtaining the optimum pressure charging effect. It will benoted that in general at higher speeds, shorter pine lengths arerequired.

on G-cylinder engines, longer branch pipes are required and on4-cylinder engines shorter ones and so on. For instance, on a 4-cylinderengine at 340 R. P. M. an additional length of pipe through which thepressure charging pulse would be propagated equivalent to 20 of crankangle is required with port timings in the earlier range given above. Onengines with fi-cylinders. or more alternatively the exhaust system maybe split up into two banks of piping in order to provide wider spacingof the pressure charging pulses so that undue lengths of exhaust branchpipes may be avoided but arranged that in general cylinders firing insequence do not exhaust into the same exhaust manifold, that is,alternating firing cylinders do exhaust into the same manifold, andpressure charging pulse from alternating cylinders are then used. Inother words, alternating cylinders, as far as one particular bank isconcerned, are

length suinciently remote from the engine to avoid interference from onebank to the other of the pulses generated therein.

I may if desired split the exhaust manifolds and pipes into more thantwo banks in order to of the 1 select the cylinders to be charged by anyparticular fundamental pressure pulses.

It will be appreciated that the exhaust pressure pulse from ily be usedfor pressure charging the cylinder which previously exhausted; forexample, the pressure pulse from one cylinder may serve for the chargingof the cylinder which exhausted next but one before. With a commonexhaust system, in say a 7-cylinder engine, as far as any one cylinderis concerned, the pressure pulse of the next cylinder in sequence whenexhausting would have a nuisance value only, as it would occur too earlyand would interrupt the scavenging period but only for a limited numberof crankshaft degrees. This might be a disadvantage but not vital; insome circumstances this interruption of the scavenging period may havethe advantageous eflect of stopping the flow of the scavenge air duringsuch part of the scavenging period as is inefficient (due to thescavenge air wastefully tending to take the shortest path from the airports in the cylinder wall to the exhaust ports).

It will be appreciated that theoretically for a given speed of engineand brake mean efiective pressure, optimum conditions can be arranged,but as soon as either of these quantities is altered, optimum conditionswillno longer obtain. In practice, however, it is possible to arrangethe various factors concerned in such a way as to provide substantialexhaust pulse pressure charging over a wide range of speeds and brakemean effective pressures.

It will be noted that this invention is not conwhich they leave thecylinder, with the pressure pulse resulting in the exhaust system at theexhausting cylinder, nor with any subsequent rarefaction or reflectedpositive or negative pulses resulting from such release.

What I claim is:

1. A method of operating a multi-cylinder twocycle internal combustionengine, controlling and re-phasing the fundamental exhaust pressurepulse from one cylinder so that it reaches a peak at or a little beforethe closing of the exhaust port of another cylinder which previouslyexhausted with the result that the latter cylinder receives a chargewhich is well above the usual air manifold pressure.

2. A method of operating a multi-cylinder twocycle internal combustionengine by controlling and rephasing the fundamental exhaust pressurepulse as claimed in claim 1 consisting in adjusting the exhaust porttiming.

3. A method of operating a multi-cylinder twocycle internal combustionengine by controlling and rephasing the fundamental exhaust pressurepulse as claimed in claim 1 consisting in varying the effective pipelengths in the exhaust system.

4. A method of operating a multi-cylinder twocycle internal combustionengine by controlling and rephasing the fundamental exhaust pressureeffective pipe lengths in the exhaust system.

5. A method of operating a multi-cylinder twocycle internal combustionengine as claimed in claim 1 consisting in adjusting the cross sectionalarea of the exhaust branches and pipe to control the amplitude of thepressure charging pulses.

6. A method of operating a multi-cylinder two- .one cylinder need notnecessar-" e 7- cycle internal combustion engine as claimed in claim 1consisting'in providing the engine with a surplus of scavenging air tofill the exhaust branch with more or less pure air which is returned tothe cylinders by means of the charging pulses.

'7. A method of operating a multi-cylinder two- I cycle internalcombustion engine as claimed in claim 1 in which the fundamental exhaustpressure pulse assists in charging a cylinder which exhausted next butone before it, utilizing such fundamental exhaust pressure pulse toassist'in stopping the flow of the scavenge air from the cylinder whichexhausted next before it during the part of the scavenging period asis'inemcient due to the scavenge air wastefuliy tending to take theshortest path from the air ports in the cylinder wall to the exhaustports therein.

8. A method of operating a two-cycle internal combustion engine havingat least three cylinders, comprising controlling and rephasing thefundamental exhaust pressure pulse from one cylinder so that it reachesthe exhaust port of another cylinder which previously exhaustedimmediately before the commencement of the compression stroke in suchcylinder and causes the pressure in the exhaust branch of such cylinderto rise to a maximum at or a little before the closing of the exhaustport, with the result that such cylinder receives a charge which is wellabove the usual air manifold pressure.

HERBERT DESMOND CARTER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name 4 Date 1,314,640 Ford Sept. 2, 19191,332,803 Charlton Mar. 2, 1920 1,394,850 Long Oct. 25, 1921 1,413,213Badger Apr. 18, 1922 1,982, 46 Sloan Nov. 27, 1934 2,305,946 Wilson eta1 Dec. 22, 1942 2,306,580 Wilson Dec. 29, 1942 FOREIGN PATENTS NumberCountry Date Great Britain 1936

